The present invention relates to printing plates suitable for imaging by digitally controlled laser radiation. More particularly, the invention relates to a printing plate having a dyed, anodized metal substrate.
Printing plates suitable for imaging by digitally controlled laser radiation include a plurality of imaging layers and intermediate layers coated thereon. Laser radiation suitable for imaging printing plates preferably has a wavelength in the visible or near-infrared region, between about 400 and 1500 nm, typically at about 830 nm. Solid state laser sources (commonly termed xe2x80x9csemiconductor lasersxe2x80x9d) are economical and convenient sources that may be used with a variety of imaging devices. Other laser sources such as CO2 lasers and lasers emitting light in the visible wavelengths are also useful.
Laser output can be provided directly to the plate surface via lenses or other beam-guiding components, or transmitted to the surface of a blank printing plate from a remotely sited laser through a fiber-optic cable. Some prior art patents disclosing printing plates suitable for imaging by laser ablation are Lewis et al. U.S. Pat. Nos. 5,339,737; 5,996,496 and 5,996,498. These prior art printing plates require multiple layers of differing materials and often are costly to produce. Accordingly, a need remains for a simple and inexpensive radiation treatable printing plate.
This need is met by the printing plate of the present invention having a metal substrate with an anodized surface portion. The surface portion defines a plurality of pores containing a radiation-absorbing composition. A coating composition covers the surface portion along with the radiation-absorbing composition. The metal may be an aluminum alloy that may be roll textured to have a roughness of about 5 to about 45 microinches.
The radiation-absorbing composition may be oleophilic while the coating composition is hydrophilic such as an acrylic polymer. A suitable acrylic polymer is a copolymer of vinyl phosphonic acid and acrylic acid cured under conditions such that said copolymer is hydrophilic or oleophilic. If the radiation-absorbing composition is hydrophilic, the coating composition may be oleophilic. Other suitable coating compositions include nickel acetate, silicate, and polyvinylphosphonic acid.
The coating composition may be ablated by radiation directed onto the coating composition overlying the radiation-absorbing composition. Alternatively, a first affinity for ink by the coating composition may change to a second affinity for ink when the coating composition overlying the radiation-absorbing composition is subjected to radiation without ablation of the coating composition.
The printing plate may further include a sealant composition disposed between the radiation-absorbing composition and the coating composition. In that case, both of the sealant composition and the coating composition overlying the radiation-absorbing composition are ablatable by radiation directed thereto. Alternatively, the sealant and coating compositions may not be ablated. Instead, a first affinity for ink by the coating composition may change to a second affinity for ink when the coating composition overlying the radiation-absorbing composition is subjected to radiation.
The present invention also includes a method of imaging having the steps of (i) providing a printing plate having a metal substrate with an anodized surface portion defining a plurality of pores, a radiation-absorbing composition received in the pores, and a coating composition covering the surface portion with the radiation-absorbing composition; and (ii) exposing the printing plate to a pattern of imaging radiation such that a first portion of the printing plate has an affinity for a printing fluid and a second portion of the printing plate has a different affinity for the printing fluid. The exposing step may include ablating the coating composition in the location of the pattern of imaging radiation to reveal the anodized surface portion as the first portion of the printing plate, the coating composition not exposed to the radiation being the second portion of the printing plate. Alternatively, the exposing step may include changing the affinity of the coating composition for a printing fluid in the location of the pattern of imaging radiation to the different affinity.